The document KR 20050102264 A (KOREA ELECTRO TECH RES INST) Oct. 26, 2005 describes the interferometer intended for testing optical surfaces and optical systems. The interferometer comprises: laser; elements of an objective of the illuminating system; inclined flat mirror, in whose reflection coating there is a pinhole aperture, whose diameter is comparable with the wavelength of radiation passing through the interferometer; tested optical element; autocollimating illuminating optical system, whose focus coincides with the pinhole aperture of the flat mirror, and after an objective of a collimator, towards to it, the objective of the second collimator is disposed, in whose focal plane an autocollimating flat mirror is disposed; an autocollimating flat mirror is fixed on the holder as a piezo-element, to whose electrodes the control electronic block is connected, the voltage from which provides reciprocating movement of a flat mirror along the optical axis; further there are established an objective, Bertran lens, projection objective of the observing system for matching the scale of the interference picture. Estonian patent No. 05614 (P200800069, Aug. 16, 2010) describes the previous solution of the inventors of the present invention and is incorporated here by reference.